A key factor in the signal transduction mechanisms underlying the actions of many drugs of abuse are the G-protein coupled receptors (GPCRs). Consequently, the structural and mechanistic information about these receptor systems is of major importance for understanding the mechanisms of action of drugs of abuse. Recently, the emerging evidence for GPCRs as homo- and hetero-oligomers suggests the need for the incorporation of these constructs into physiologically relevant functional models of these receptors. The overall goal of the present grant application is to develop, interpret and disseminate to the scientific community detailed information about the structural context of GPCR dimerization and its experimentally determined implication for mechanisms of drugs of abuse. We plan to use Bioinformatics methods to determine homo- and hetero-dimerization interfaces of GPCRs relevant to mechanisms of drugs of abuse, and to construct an Information Management System (IMS) designed to store such data and its cognate context in a manner that will facilitate the design and interpretation of pointed physiological and pharmacological experiments. Based on the recent evidence that some GPCRs interact with one type of receptors, but not another, the working hypothesis of this R21 phase of the present R21/R33 application is that dimerization interfaces may vary among different receptor subtypes. In order to identify the most likely dimerization interfaces of GPCRs involved in mechanisms of drugs of abuse, we will use a recently developed Bioinformatics approach that identifies correlated mutations on the receptor lipid-facing region from multiple sequence alignments of specific GPCR subfamilies. The predicted interfaces will then be used to guide the molecular modeling of GPCR homo- and hetero-dimers involved in mechanisms of drugs of abuse. The information available from each of these monomer-based models will guide key collaborative experiments that will serve to probe, validate, and eventually refine the GPCR dimeric models during the R33 phase of this R21/R33 application. Thus, the information about the dimerization interface obtained from real dimers, rather than the GPCR monomers used in the initial models, will populate the database of the IMS in the R33 phase. Several leading experts in the field of GPCRs have already expressed their enthusiasm and support for the work proposed here, as stated in the attached letters of collaboration, and will provide the pilot data for populating the experimental information and context in the IMS.